Magnetic recording medium and magnetic recording apparatus using the same

ABSTRACT

Magnetic recording medium includes at least two layers having different magnetic anisotropy constants formed on a substrate and the perpendicular magnetic anisotropy of the second magnetic film of those magnetic films, far from the substrate surface, made equal to or larger than that of the first magnetic film near to the substrate surface, thus improving the magnetic isolation.

This application is a continuation of application Ser. No. 09/379,462,filed Aug. 24, 1999, now U.S. Pat. No. 6,403,203, which is a division ofapplication Ser. No. 09/085,861, filed May 28, 1998 now abandoned, whichare incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to perpendicular magnetic recording mediumwhich are small in read back noise and suitable for high-densitymagnetic recording, and to a magnetic recording apparatus using thesemedia.

BACKGROUND OF THE INVENTION

The currently used practical magnetic recording system is thelongitudinal magnetic recording system in which magnetic recording ismade in parallel to the surface of the magnetic recording medium, and sothat the magnetic N-poles are opposed one to one and that the magneticS-poles are opposed to one to one. In order to increase the linearrecording density in the longitudinal magnetic recording, it isnecessary that the coercivity be increased by decreasing the product ofresidual flux density (Br) and magnetic film thickness (t) of themagnetic film of a recording medium to reduce the effect of thedemagnetizing field at the magnetic recording process. In addition, todecrease the medium noise caused by magnetization transition, it isnecessary to orient the magnetic easy axis of the magnetic film in thedirection parallel to the substrate surface, and to control the crystalgrain size. To control the crystal orientation and grain size of themagnetic thin film, an underlayer for structure control is formedbetween the substrate and the magnetic film.

As the magnetic film, a Co-based alloy thin film is used which chieflycontains cobalt Co, and has an element such as Cr, Ta, Pt, Rh,.Pd, Ti,Ni, Nb, Hf added to the cobalt. The Co-based alloy of the magnetic thinfilm is chiefly made of a material of hexagonal closed packed structure(hereinafter, referred to as hcp structure). The magnetic easy axis ispresent in the directions of c-axis, <0, 0.1> and is oriented in thelongitudinal direction. An underlayer for structure control is formedbetween the substrate and the magnetic film in order to control thecrystal orientation and grain size of the magnetic film. The underlayeris made of a material which chiefly contains Cr and has an element ofTi, Mo, V, W, Pt, Pd added to Cr. The magnetic thin film is formed byvacuum evaporation or sputtering. As described above, the product ofresidual flux density (Br) and magnetic film thickness (t) of themagnetic film is required to be reduced in order to reduce the mediumnoise in the longitudinal magnetic recording and to thereby increase thelinear recording density. For this purpose, it has been considered thatthe magnetic film thickness is reduced to 20 nm or below, and that thecrystal grain size is greatly reduced. However, such medium has a veryimportant problem that the recording magnetization is reduced by thermalinstability. This phenomenon interferes with the high density recording.

The presently used magnetic disk recording apparatus is of thelongitudinal magnetic recording system. The technical subject is thatthe longitudinal domains parallel to the substrate are formed at highdensity in the longitudinal magnetic recording medium which is easy tobe magnetized in the direction parallel to the disk substrate surface. Amethod of increasing the recording density in the longitudinal magneticrecording medium is proposed, which employs keepered media formed bydepositing an extremely thin soft magnetic film on the recording mediumthat have the magnetic easy axis in the longitudinal direction.

This technique is described in Abstracts, page 116 (paper No. DQ-13) andpages 133-134 (paper No. EB12) published in the 41st Annual Conferenceon Magnetism & Magnetic Materials (Nov. 12-15, 1996).

In such documents, it is described that if this media structure isemployed it will be possible to increase the longitudinal magneticrecording density to 1 Gb/in2 or above by use of thin film heads ofself-recording/reproduction system. In the longitudinal recordingsystem, however, since the adjacent recorded bits are substantiallymagnetized to oppose to each other, magnetization transition regions ofcertain widths are formed across the boundaries even when this techniqueis employed. Thus, it will be technically difficult to record at alongitudinal density of 5 Gb/in2 or above.

On the other hand, the perpendicular magnetic recording system formsdomains on the recording medium surface perpendicularly, and so that theadjacent recorded bits are unti-parallel to each other. This system hasthe advantage that the demagnetizing field at the boundary between therecorded bits is decreased, and thus it is one of the powerful means forhigh-density magnetic recording.

For the longitudinal high-density recording, it is necessary that themagnetic film be formed to have a thickness of 20 nm or below asdescribed above. In this case, there is a problem that the recordedmagnetization regions may be lost by thermal instability. On thecontrary, the perpendicular magnetic recording system is able to formthe magnetic film thicker than the longitudinal magnetic recordingsystem, and thus stably maintain the recorded magnetization regions. Inorder to reduce the media noise generated from the magnetizationtransition and increase the linear recording density in theperpendicular recording system, it is necessary to orient the magneticeasy axis of the magnetic film perpendicularly to the substrate surface,and control the crystal grain size.

As the magnetic film, a Co-based alloy thin film is used which chieflycontains cobalt Co and has an element of Cr, Ta, Pt, Rh, Pd, Ti, Ni, Nb,Hf added to Co. The Co-based alloy of the magnetic thin film is chieflymade of a material of hexagonal closed packed structure (hereinafter,referred to as hcp structure). The magnetic easy axis is present in thedirections of c-axis, <0, 0.1> and is oriented in the perpendiculardirection. The magnetic thin film is formed by vacuum evaporation orsputtering. In order to increase the linear recording density at thetime of recording and the read output and reduce the read back noise sothat the magnetic recording characteristics can be improved, it isnecessary to improve the perpendicular orientation of the c-axis of theCo-based alloy thin film and control the crystal grain size. Thus, ithas so far been considered that an underlayer for structure control isformed between the substrate and the magnetic film.

The perpendicular magnetic recording system has attracted a great dealof attention as a system capable of high-density magnetic recording, andstructure of medium suitable for the perpendicular magnetic recordinghave been proposed. A method of providing a non-magnetic underlayerbetween the perpendicular magnetization film and the substrate has beenexamined in order to improve the perpendicular orientation of theperpendicularly magnetized film made of a Co-based alloy material. Forexample, a method of depositing a Ti film as an underlayer for a Co—Crmagnetic film is described in JP-A-5877025, and JP-A-58-141435, a methodof providing an under layer made of Ge, Si material in JP-A-60-214417,and a method of providing an underlayer made of an oxide material suchas CoO, NiO in JP-A-60-064413. In addition, a magnetic recording mediumhaving a soft magnetic layer of Parmalloy provided between the substrateand the perpendicular magnetization film has been considered as aperpendicular magnetic recording medium which is used in combinationwith a single-pole type magnetic recording head.

However, in order to achieve ultra-high density magnetic recording ofseveral Gb/in² or above, particularly more than 10 Gb/in², it isimportant to reduce the noise contained in the read output signal,particularly the medium noise caused by the micro-structure of themedium in addition to the improvement of the linear recording density.Thus, it is necessary to more highly control the thin film structure inaddition to the crystal orientation of the magnetic film. The medianoise has so far been tried to reduce by various ways. For example,these ways are (1) to segregate the nonmagnetic element Cr of CoCr-basedalloy in the crystal grain boundary or grains in order to suppress themagnetic mutual action between the magnetic grains and (2) to isolatethe magnetic grains in a form by controlling the sputtering gaspressure. The improvement in medium structure by these conventionaltechniques was effective in reducing the medium noise, but the reversemagnetic domains formed opposite to the magnetization direction and theassociated magnetization irregularity, which cause the medium noise inthe perpendicular magnetic recording, was not able to be reducedeffectively.

The perpendicular magnetic recording medium capable of high-densitymagnetic recording of 5 Gb/in² or above is required to have small mediumnoise in addition to high linear recording density or resolution. Thereare some reported examples. As for example described in a paper titled“Improvement in S/N ratio of Single Layer Perpendicular Magnetic DiskMedia” of the Fifth Perpendicular Magnetic Recording Symposium (Oct.23-25, 1996), pp. 98-103, it is effective to decrease the thickness ofthe perpendicular magnetization film, introduce a non-magneticunderlayer of CoCr between the perpendicular magnetization film and thesubstrate, add a non-magnetic element such as Ta to the Co alloymagnetic film and/or reduce the magnetic crystal grain size. Thesecountermeasures are able to considerably reduce the medium noise, but ifthe noise can be more decreased, the recording density of the magneticrecording apparatus will be easily increased much more.

Accordingly, it is an object of the invention to remove the drawbacks ofthe prior art, and provide perpendicular magnetic recording media havingexcellent-low-noise characteristics and suitable for ultra-high densitymagnetic recording by controlling the perpendicular magnetic anisotropy,crystal orientation or mutual action between the magnetic grains of theperpendicular magnetization film formed on the substrate to therebycontrol the fine domain structure magnetically recorded, and a magneticrecording apparatus using the medium.

According to the invention, the perpendicular magnetic recording mediumhaving the low-noise characteristics can achieve high-density recordingof 5 Gb/in² or above, and thus make it easy to produce high-densityrecording apparatus.

After examining the recorded magnetization structure of theperpendicular magnetic recording medium by a magnetic force microscopeand a spin-polarized scanning electron microscope, it was found thatmost of the noise are caused by reverse magnetic domains and microscopicinstability of magnetization present in the medium surfaces. In order todecrease the medium noise, it is necessary to reduce the reversemagnetization and microscopic instability of magnetization present inthe medium surfaces.

SUMMARY OF THE INVENTION

It is an object of the invention to provide perpendicular magneticrecording medium having both low noise characteristics and high-densitylinear recording characteristic which enable the high-densitymagnetic-recording of 5 Gb/in² or above, and magneticrecording/reproducing apparatus using the medium.

According to the invention, at least two magnetic films which aredifferent in perpendicular magnetic anisotropy are formed on thesubstrate, and in this case the perpendicular magnetic anisotropy of thesecond magnetic film on the side far from the substrate is made greaterthan that of the first magnetic film on the side near to the substratesurface, thereby improving the magnetic isolation of the first magneticfilm on the side near to the substrate surface. That is, the aboveobject can be achieved by assigning a different role to each magneticfilm as they say.

After examining the recorded magnetization structure by a magnetic forcemicroscope or spin polarized scanning electron microscope, it was foundthat most of the noise are caused by the reverse magnetic domains andmicroscopic instability of magnetization present in the medium surfaces.In order to decrease the medium noise, it is necessary to reduce thereverse magnetic domains and microscopic instability of magnetizationpresent in the medium surfaces. To decrease the medium noise and assurehigh-density linear recording characteristics, it is desired to reducethe magnetic crystal grain size of the perpendicular magnetic recordingmedium and magnetically isolate the grains.

From the results of experiments by the inventors, it was found that thefollowing media structure is effective in achieving the above object.

First, referring to FIG. 1, a single-layer type perpendicular magneticrecording medium is normally produced by depositing a perpendicularmagnetization film 13 on an underlayer 12 which is formed on anon-magnetic substrate 11 for the purpose of improving the perpendicularorientation of the magnetic film and controlling the crystal grain size.On this magnetization film, there is usually deposited a protective filmof carbon or the like. The magnetic film is made of a Co-based alloycontaining at least one element selected from Cr, Ta, Pt, Pd, Si, V, Nb,W, Mo, Hf, Re, Zr, B, P, Ru. This magnetic film is a polycrystallinefilm, and for high density linear recording characteristic and low-noisecharacteristic, its crystal grain size is selected to be normally 20 nmor below, and a non-magnetic element is preferentially segregated in thecrystal grain boundary. This perpendicular magnetization film has asmall magnetic exchange coupling force in the longitudinal directionbecause the segregated layer exists in the crystal grain boundary.

The present inventors found that the effective way to further reduce themedium noise is to provide on the first perpendicular magnetization film13 of Co-based alloy a second perpendicular magnetization film 14 ofwhich the magnetic exchange coupling force in the longitudinal directionis greater than that of the first perpendicular magnetization film. Thesecond perpendicular magnetization film 14 is preferably a multi-layeredperpendicular magnetization film of Co/Pt, Co/Pd, Co alloy/Pt, Coalloy/Pd, Co alloy/Pt or Pd alloy or a noncrystal perpendicularmagnetization film of Tb Fe Co containing rare-earth elements.

The deposition of the second perpendicular magnetization film 14 canreduce the magnetic instability present in the surface of the firstperpendicular magnetization film 13. Since the second perpendicularmagnetization film 14 has a large magnetic exchange coupling force inthe longitudinal direction, the microscopic magnetic instability is noteasily caused on the surface.

Here, in order to assure low-noise characteristics in the perpendicularmagnetic recording medium, it is necessary to decrease the thickness ofthe second perpendicular magnetization film 14 as compared with that ofthe first perpendicular magnetization film 13. The thickness of thesecond perpendicular magnetization film is preferably selected to beless than ⅓ that of the first perpendicular magnetization film. The roleof the second perpendicular magnetization film 14 is not to hold theperpendicular magnetic recording, but to greatly reduce the microscopicmagnetic instability in the surface of the first perpendicularmagnetization film 13. To assign this function to a thin film, it ismore desirable to provide high magnetic anisotropy energy of 5×10⁶erg/cc or above. When the thickness of the second perpendicularmagnetization film 14 is larger than that of the first perpendicularmagnetization film 13, the medium noise is increased as compared withthe case in which only the first perpendicular magnetization film isdeposited.

In order to achieve a recording density of 5 Gb/in² or above, the totalthickness of the first and second perpendicular magnetization filmsshould be selected to be more than 7 nm and less than 100 nm. If thetotal thickness is larger than 100 nm, the magnetic crystal grainsconstituting the perpendicular magnetization films are enlarged involume, and as a result the magnetic switching volume is also increased,thus causing large medium noise. Accordingly, it is not possible toachieve the signal to noise ratio for a recording density of 5 Gb/in² orabove. If the total thickness is equal to or less than 7 nm, therecording magnetization is remarkable deteriorated by thermalinstability.

The thickness of the second perpendicular magnetization film ispreferably more than 3 nm and less than 10 nm. If it is equal to or lessthan 3 nm, the effect of reducing the magnetic instability in thesurface of the first perpendicular magnetization film is unrecognizablysmall. If it is larger than 10 nm, the medium noise is increased.

The object of the invention can also be achieved by employing thestructures shown in FIGS. 2 through 6. As to the structure shown in FIG.2, the second perpendicular magnetization film 14 is deposited on thefirst perpendicular magnetization film 13 as in the case of FIG. 1, butbetween the first perpendicular magnetization film 13 and thenon-magnetic substrate 11 there are formed an underlayer 23 of anonmagnetic material having a hexagonal closed packed structure or aweak ferro magnetic material having a hexagonal closed packed structureof which the saturation magnetization is 100 emu/cc or below, and theunderlayer 12 for controlling the crystal orientation of this underlayerfilm. Use of these dual-underlayer structure will enable the firstperpendicular magnetization film to be highly controlled in its crystalgrain size and orientation, and low-noise characteristics to beachieved.

The media structure, as shown by its cross section in FIG. 3, has thefirst and second perpendicular magnetization films 13, 35 stacked, andalso has another perpendicular magnetization film 33 of multi-layeredstructure or non-crystal structure formed between the firstperpendicular magnetization film 13 and the underlayer 12. Thus, themagnetic instability present in the front and back sides of the firstperpendicular magnetization film 13 can be reduced, so that low-noisecharacteristics can be achieved.

The cross-sectional structures shown in FIGS. 4 through 6 are structuresof perpendicular magnetic recording media of the type in which a softmagnetic layer is provided under the perpendicular magnetization film asindicated by reference numeral 42. In this case, the secondperpendicular magnetization film 44 of multi-layered structure oramorphous-like structure is also provided on the first perpendicularmagnetization film 13 of Co alloy.

Referring to FIG. 5, there is shown an underlayer film 53 having anon-magnetic hexagonal closed packed structure or a weak ferro magnetichexagonal closed packed structure of which the saturation magnetizationis 100 emu/cc or less. In FIG. 6, there is shown a perpendicularmagnetization film 64 of multi-layered or amorphous structure.

The second perpendicular magnetization film of multi-layered oramorphous structure is formed on the first perpendicular magnetizationfilm as shown in FIGS. 1 through 6. This second perpendicularmagnetization film serves to reduce the microscopic magnetic instabilitypresent in the surface of the first perpendicular magnetization film.The perpendicular magnetization film of multi-layered or non-crystalstructure formed under the first perpendicular magnetization film asshown in FIGS. 3 and 6 acts to reduce the microscopic magneticinstability present in the lower surface of the first perpendicularmagnetization film.

The underlayer 12 in FIG. 1, the underlayer film 23, shown in FIG. 2, ofnon-magnetic hexagonal closed packed structure or weak ferro magnetichexagonal closed packed structure of which the saturation magnetizationis 100 emu/cc or below, the underlayer 12 formed thereunder, theunderlayer shown in FIG. 3, the under layer 53, shown in FIG. 5, ofnon-magnetic hexagonal closed packed structure or weak ferro magnetichexagonal closed packed structure of which the saturation magnetizationis 100 emu/cc or below, and the underlayer 12 in FIG. 6 are all providedfor the purpose of controlling the crystal orientation and crystal grainsize of the magnetic films formed on these underlayers, respectively,thus making it possible to improve the characteristics of the magneticfilms along their purposes. If the saturation magnetization of theunderlayer film exceeds 100 emu/cc, the medium noise will be increased,and the recording resolution will be reduced, thus adversely affectingthe magnetic recording/reproduction characteristics.

As to the cause of the reverse magnetic domain, if the perpendicularmagnetization film is perpendicularly magnetized in one direction, anintense demagnetizing field is acted on the medium surface, and thisaction of demagnetizing field produces the so-called reverse magneticdomains in the direction opposite to the perpendicularly magnetizeddirection. In order to suppress this reverse magnetic domains from beingproduced, it is necessary to employ a perpendicular magnetization filmhaving magnetic anisotropy energy. The magnetic anisotropy energy isdesirably 2.5×10⁶ erg/cc or above.

The magnetic anisotropy energy of the perpendicular magnetization filmmade of Co-based alloy easy to handle as practical media is 5×10⁶erg/cc. There is a Co-based alloy regular lattice material having moremagnetic anisotropy energy than this value, but this material hasdifficulty in reducing noise because too large media noise is caused bya strong mutual action in the longitudinal direction of the magneticfilm.

The multi-layered perpendicular magnetization film of Pt/Co, Pd/Co otherthan Co alloy or a perpendicular magnetization film of amorphousstructure containing rare earth elements such as TbFeCo hasmagnetic-anisotropy energy of 2.5×10⁶ erg/cc or above and thus can beexpected to attain the present subject. However, the magnetic mutualaction in the longitudinal direction will also be strong as in the abovedescription if no countermeasure is provided, and hence the medium noiseis large. Thus, a special device is needed for reducing the media noise.In addition, in order to increase the surface magnetic recording densityup to 5 Gb/in² or above, the linear recording density is required to be250 kFCI or above. The bit length corresponding to this linear recordingdensity is 100 nm. The thickness of the magnetic recording media forrecording is desired to be less than the minimum bit length. Thus, thethickness of the perpendicular magnetization film is required to be 100nm or below.

Since the reverse magnetic domains can be suppressed by use of aperpendicular magnetization film of high magnetic anisotropy energy, themedium noise due to the reverse magnetic domains can be prevented frombeing produced. However, the medium noise is also produced by amicroscopic magnetic instability present in the medium surfaces. If themagnetic mutual action in the longitudinal direction of the magneticfilm is large, a long-period magnetizing instability is produced. Inaddition, it was found that if there is magnetic heterogeneity in thesurface of the perpendicular magnetization film, a short-periodmagnetizing instability is produced, thus causing the medium noise.

From the results of the experiments by the inventors, it was found thatin order to suppress these long-period, short-period magneticinstability, it is necessary that a soft magnetic film or a magneticfilm having a magnetic easy axis in the longitudinal direction be formedon the surface of the perpendicular magnetization film. In this case,the thickness of the magnetic films must be selected to be smaller thanthat of the perpendicular magnetization film for recording. If the filmthickness is large, the magnetic flux produced from the recorded bits onthe perpendicular magnetization films makes closed magnetic circuitsabsorbed by these films, and thus the magnetic flux does not leak fromthe medium surfaces, so that the recorded signal cannot be reproduced bymagnetic heads.

If the thickness of these magnetic films is properly thin, thelong-period, short-period magnetic instability present in theperpendicular magnetization film surfaces is absorbed by the magneticfilms formed on the surfaces of the perpendicular magnetization films,but the strong magnetic flux generated from the recorded bits cannot beabsorbed enough. In this case, since the magnetic flux caused by themagnetic instability does not leak to the magnetic film surfaces, itcannot be detected by magnetic heads, so that the medium noise isdecreased. The combination of the perpendicular magnetization film whichabsorbs the magnetic flux due to the magnetic instability but littleabsorbs the magnetic flux from the recorded bits, and the thickness ofthe magnetic film provided on the surface depends on the thickness ofthe perpendicular magnetization film, saturation magnetization,coercivity and so on. Thus, it is necessary to select the most suitablecombination for each case.

The thickness of the magnetic film provided on the surface should beconfined within a range of generally 2 to 10 nm or preferably 3 to 5 nmconsidering the factors such as controllable ability for film productionand for film thickness distribution in all regions of disk surfaces. Themagnetic film may be a soft magnetic film of Parmalloy, Fe—Si, Fe—Si—Al,CoNbZr or other materials or a magnetic film, of Co, Ni, Fe, CoNi,CoNiCr or the like, which is easy to be magnetized in the longitudinaldirection. In addition, part of the surface of the perpendicularmagnetization film may be changed to a soft magnetic film orlongitudinal magnetization film by diffusing or implanting a lightelement such as C, B, N or P into the surface.

FIG. 7 shows an example of the application of the invention to asingle-layered perpendicular magnetic recording medium.

In this single-layered perpendicular magnetic recording medium, normallythe underlayer 12 for improving the perpendicular orientation of themagnetic film and controlling the crystal grain size is deposited on thenon-magnetic substrate 11, and a perpendicular magnetization film 71 isformed on the underlayer. In addition, a protective film of carbon orthe like is normally deposited on the magnetization film.

The magnetic film 71 is made of a Co-based alloy containing at least oneof Cr, Ta, Pt, Pd, Si, V, Nb, W, Mo, Hf, Re, Zr, B, P, Ru. This magneticfilm is a poly-crystal film of which the crystal grain size is normally20 nm or below and which has the structure in which a non-magneticelement is preferentially segregated in the crystal grain boundaries inorder to attain high density linear recording characteristics and lownoise characteristic. This perpendicular magnetization film has a smallmagnetic exchange coupling force because of the presence of thesegregated layer in the crystal grain boundaries, and a microscopicmagnetic instability because of the compositional segregation andundulations in the media surfaces.

To reduce the medium noise, a soft magnetic film or longitudinalmagnetization film 72 which is thinner than the thickness of theperpendicular magnetization film is deposited on the perpendicularmagnetization film 71. The perpendicular magnetization film 71 may be amulti-layer type perpendicular magnetization film made of Co/Pt, Co/Pd,Co alloy/Pt, Co alloy/Pd, Co alloy/Pt or Pd alloy, or a amorphous typeperpendicular magnetization film containing a rare earth element such asTbFeCo in place of being made of a Co-based alloy material.

When the soft magnetic film 72 is provided on the perpendicularmagnetization film 71, the magnetic flux generated from the magneticinstability present in the surface of the perpendicular magnetizationfilm 71 is absorbed by the magnetic film, and as a result the mediumnoise is decreased. In addition, when a thin magnetic film is formed,the magnetic instability is not easily generated even if microscopicundulations and composition segregation are present in the surface. Asshown in FIG. 7, the protective film 15 is deposited on themagnetization film.

In order to achieve a recording density of 5 Gb/in² or above, the totalthickness of the perpendicular magnetization film 71 and soft magneticfilm 72 is required to be confined within the range of 7 nm to 100 nm.If the thickness is larger than 100 nm, the volume of magnetic crystalgrain constituting the film becomes large, and as a result the magneticswitching volume is enlarged. Thus, the medium noise is increased,degrading the signal to noise ratio, so that a recording density of 5Gb/in² or above cannot be attained. If the thickness is smaller than 7nm, the recording magnetization is remarkably deteriorated by thermalinstability.

The object can also be achieved by use of the structures shown in FIGS.8 through 10. In the medium structure shown in FIG. 8, an underlayer 73having a nonmagnetic hexagonal closed packed structure or a weak ferrohexagonal closed packed structure of 100 emu/cc or below is formedbetween the first perpendicular magnetization film 71 and thenon-magnetic substrate 11, and the underlayer 12 is also formed underthe underlayer 73 in order to control the crystal grain orientation ofthe underlayer film 73. In addition, the magnetic film 72 made of a thinsoft magnetic film or longitudinal magnetization film is deposited onthe perpendicular magnetization film 71. By this dual underlayerstructure, it is possible to highly control the crystal grain size andcrystal orientation of the perpendicular magnetization film, and henceto attain low noise characteristics.

The structures shown by the cross-sectional views of medium of FIGS. 9and 10 are of the perpendicular magnetic recording medium of the type inwhich a soft-magnetic film layer is held under the perpendicularmagnetization film. As shown in FIGS. 9 and 10, a soft magnetic filmlayer 74 is formed on the substrate. In this case, the magnetic film 72of a soft magnetic film or having longitudinal magnetic anisotropy isalso formed on the perpendicular magnetization film.

In FIGS. 7 through 10, the magnetic film formed on the perpendicularmagnetization film absorbs the magnetic flux generated from thelong-period, short period magnetic instability present in the surface ofthe perpendicular magnetization film, thus serving to reduce the mediumnoise. The underlayer 12 in FIG. 7, the underlayer 73 having anon-magnetic hexagonal closed packed structure or a weak ferro hexagonalclosed packed structure of which the saturation magnetization is 100emu/cc or below, and the underlayer 12 under it as shown in FIG. 8, andthe underlayer 73 in FIG. 10 are all provided for the purpose ofcontrolling the crystal orientation and crystal grain size of themagnetic film formed on the underlayers. Thus, the magnetic film can beimproved in the characteristics.

In addition, the protective film 15 is formed as shown in the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of one embodiment of a magneticrecording medium according to the invention.

FIG. 2 is a cross-sectional view of another embodiment of a magneticrecording medium according to the invention.

FIG. 3 is a cross-sectional view of another embodiment of a magneticrecording medium according to the invention.

FIG. 4 is a cross-sectional view-of another embodiment of a magneticrecording medium according to the invention.

FIG. 5 is a cross-sectional view of another embodiment of a magneticrecording medium according to the invention.

FIG. 6 is a cross-sectional view of another embodiment of a magneticrecording medium according to the invention.

FIG. 7 is a cross-sectional view of another embodiment of a magneticrecording medium according to the invention.

FIG. 8 is a cross-sectional view of another embodiment of a magneticrecording medium according to the invention.

FIG. 9 is a cross-sectional view of another embodiment of a magneticrecording medium according to the invention.

FIG. 10 is a cross-sectional view of another embodiment of a magneticrecording medium according to the invention.

FIG. 11A to FIG. 11F are diagrams to which reference is made inexplaining a magnetic recording medium of the invention.

FIG. 12A to FIG. 12F are diagrams for comparing a magnetic recordingmedium of the invention and conventional media.

FIG. 13A and FIG. 13B are plan views and cross-sectional view of anembodiment of a magnetic recording apparatus according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[Embodiment 1]

The magnetic recording medium having the cross section shown in FIG. 1was produced by depositing films on a glass substrate of 2.5-inchdiameter according to DC magnetron sputtering method. On the substrate11, there were formed in turn the underlayer 12, the first perpendicularmagnetization film 13, the second perpendicular magnetization film 14,and the protective film 15. The underlayer was deposited by use of aTi-10 at % Cr target, the first perpendicular magnetization film by aCo-19 at % Cr-8 at % Pt target, the second perpendicular magnetizationfilm by a target of Co and Pt, and the protective film by a carbontarget.

Under the conditions of a sputtering Ar gas pressure of 3 m Torr,sputter power of 10 W/cm², and substrate temperature of 250° C., a TiCrfilm was formed up to a thickness of 30 nm, the first perpendicularmagnetization film up to 30 nm, a Co/Pt multi-layered film of the secondperpendicular magnetization film up to 6 nm, and the carbon film up to10 nm. As to the Co/Pt multilayered film of the second perpendicularmagnetization film, a Co target and a Pt target were alternatelyoperated to grow a film of 1.5 nm in each part of one cycle, and thusthe total thickness, 6 nm of the second perpendicular magnetization filmwas grown in two cycles. Thus, the magnetic recording medium of whichthe cross section is shown in FIG. 1 was produced. Here, the anisotropyenergy of the first perpendicular magnetization film was 3×10⁶ erg/cc,and the anisotropy energy of the second perpendicular magnetization filmwas 2×10⁷ erg/cc.

In addition, as the second perpendicular magnetization film,multi-layered films of Co/Pd, Co-16 at % Cr/Pt, and Co/Pt-20 at % Pdwere grown up to the same thickness and structure as given above. Theperpendicular magnetization film of TbFeCo was also formed to have thesame thickness. Thus, different magnetic recording medium were produced.The anisotropy energy of the second perpendicular magnetization film foreach case was 1×10⁷ erg/cc for Co/Pd, 1.2×10⁷ erg/cc for CoCr/Pt, 8×10⁶erg/cc for Co/PtPd, and 6×10⁶ erg/cc for TbFeCo. More-over, magneticrecording medium of the same structure, but having no secondperpendicular magnetization film were produced as samples forcomparison.

The coercivity (Hc) and read/write characteristics of these magneticrecording medium were evaluated by a vibrating sample magnetometer (VSM)and a dual head with inductive head for writing and withmagnetoresistive (MR) head for reading. The gap length of the recordhead was selected to be 0.2 μm, the shield gap length of the MR head forreading to be 0.2 μm, and the spacing for measurement to be 0.06 μm. Thehalf output decoding density (D₅₀), which corresponds to the half of thelow-frequency read output, was measured. The signal to noise ratio, S/Nratio for magnetic recording at 20 kFCI was measured relative to the S/Nratio of the samples for comparison. The measured results are shown inTable 1.

TABLE 1 EXAMPLES FOR INVENTION COMPARISONS UNDERLAYER Ti—Cr Ti—Cr FIRSTPERPENDICULAR FILM CoCrPt CoCrPt SECOND PERPENDICULAR FILM Co/Pt Co/PdCoCr/Pt Co/PtPd TbFeCo No COERCIVITY (kOe) 3.2 2.7 2.8 2.6 2.9 2.5RECORDING DENSITY D₅₀ (kFCI) 210 225 208 245 240 180 S/N (RELATIVEVALUE) 1.8 1.9 2.3 2.1 1.7 1

From the table, it was found that the magnetic recording medium of thisembodiment have larger D₅₀ and S/N than the samples for comparison andthus can be used as high-density magnetic recording medium. In addition,a magnetic recording/reproducing apparatus with MR head for reading wasproduced which employs the 2.5-in diameter magnetic recording media madeaccording to this embodiment. This apparatus was operated under thecondition of 5.7 Gb/in² in areal density. The result was that the errorrate can be confined within 1×10⁻⁹. Thus, it was confirmed that thisapparatus can be used as ultrahigh density magneticrecording/reproducing apparatus.

[Embodiment 2]

The magnetic recording medium having the cross-section shown in FIG. 2was produced by depositing films on a 2.5-in diameter silicon substrateaccording to the DC magnetron sputtering method. On the substrate 11,there were formed in turn the first underlayer 12, the second underlayer23, the first perpendicular magnetization film 13, the secondperpendicular magnetization film 14 and the protective film 15. Thefirst underlayer was deposited by use of a Ti-10 at % Cr target, thesecond underlayer by a Co-35 at % Cr target, the first perpendicular.magnetization film by a Co-16 at % Cr-8 at % Pt-3 at % Ta target, thesecond perpendicular magnetization film by a target of Co and Pt, andthe protective film by a carbon target.

Under the conditions of a sputtering Ar gas pressure of 3 m Torr,sputter power of 10 W/cm², and substrate temperature of 280° C., a CrTifilm was formed up to a thickness of 30 nm, a CoCr film up to 15 nm, thefirst perpendicular magnetization film up to 25 nm, a Co/Ptmulti-layered film of the second perpendicular magnetization film up to6 nm, and the carbon film up to 10 nm. As to the Co/Pt multi-layeredfilm of the second perpendicular magnetization film, a Co target and aPt target were alternately operated to grow a film of 1.5 nm in eachpart of one cycle, and thus the total thickness, 6 nm of the secondperpendicular magnetization film was grown in two cycles. Thus, themagnetic recording medium of which the cross-section is shown in FIG. 2was produced. The saturation magnetization of the Co—Cr film formed asthe second underlayer was 25 emu/cc, and the anisotropy energy of thesecond perpendicular magnetization film 14 was 2×10⁷ erg/cc.

Magnetic recording media of the same structure but having no secondperpendicular magnetization film were produced as samples forcomparison.

The coercivity (Hc) and read/write characteristics of these magneticrecording media were evaluated by a vibrating sample magnetometer (VSM)and a dual head with inductive head for writing and withmagnetoresistive (MR) head for reading. The gap length of the recordhead was selected to be 0.2 μm, the shield gap length of the giantmagnetoresistive (GMR) head for reading to be 0.15 μm, and the spacingfor measurement to be 0.04 μm. The half output recording density (D₅₀)was measure. The signal to noise ratio, S/N ratio for magnetic recordingat 20 kFCI was measured relative to the S/N ratio of the samples forcomparison. The measured results are shown in Table 2.

TABLE 2 EXAMPLES FOR INVENTION COMPARISON FIRST UNDERLAYER Ti—Cr Ti—CrSECOND UNDERLAYER CoCr CoCr FIRST PERPENDICULAR FILM CoCrPtTa CoCrPtTaSECOND PERPENDICULAR FILM Co/Pt No COERCIVITY He (kOe) 3.5 2.6 RECORDINGDENSITY D₅₀ (kFCI) 260 190 S/N (RELATIVE VALUE) 2.3 1

From the table, it was found that the magnetic recording medium of thisembodiment have much larger D₅₀ and S/N than the samples for comparisonand thus can be used as high-density magnetic recording media. Inaddition, a magnetic recording/reproducing apparatus with GMR head forreading was produced which employs the 2.5-in diameter magneticrecording medium made according to this embodiment. This apparatus wasoperated under the condition of 8 Gb/in² in areal density. The resultwas that the error rate can be confined within 1×10⁻⁹. Thus, it wasconfirmed that this apparatus can be used as ultra-high density magneticrecording/reproducing apparatus.

[Embodiment 3]

A perpendicular magnetization film of Co/Pt multi-layered film 6 nmthick was provided in place of the second underlayer in the magneticrecording media of embodiment 2. The other portions were made the sameas above. The produced magnetic recording medium have thecross-sectional structure shown in FIG. 3. In other words, on the 2.5-indiameter substrate 11, there were formed in turn the underlayer 12 ofCrTi film 30 nm thick, the perpendicular magnetization film 33 of Co/Ptmulti-layered film 6 nm thick, the first perpendicular magnetizationfilm 13 of CoCrPtTa film 25 nm thick, the second perpendicularmagnetization film 35 of Co/Pt multi-layered film 6 nm thick, and theprotective film 15 of carbon film 10 nm thick.

Magnetic recording media with no second perpendicular magnetization filmof Co/Pt multi-layered film under the protective film 15 were alsoproduced as samples for comparison.

As a result of comparing the measurements under the same read/writeconditions as in Embodiment 2, it was confirmed that the magneticrecording media according to the invention have excellent D₅₀ and S/Nwhich are 20%, 75% higher than the samples for comparison.

[Embodiment 4]

The magnetic recording medium having the cross-section shown in FIG. 4was produced by depositing on a glass substrate of 2.5-inch diameteraccording to DC magnetron sputtering method. On the substrate 11, therewere formed in turn the soft magnetic layer 42, the multi-layeredperpendicular magnetization film 43, the first perpendicularmagnetization Co-alloy film 13, the second perpendicular magnetizationmulti-layered film 44 and the protective film 15. The soft magneticlayer was deposited by use of a Fe-80 at % Ni target, the multilayeredperpendicular magnetization film by a target of Co and Pt, the firstperpendicular magnetization film of Co alloy by a Co-19 at % Cr-8 at %Pt target, the multilayered second perpendicular magnetization film byCo, Pt target and the protective film by a carbon target.

Under the conditions of a sputtering Ar gas pressure of 3 m Torr,sputter power of 10 W/cm², and substrate temperature of 250° C., a FeNifilm was formed up to a thickness of 30 nm, a Co/Pt multi-layered filmof perpendicular magnetization film up to 6 nm, a CoCrPt perpendicularmagnetization film up to 30 nm, a Co/Pt multi-layered perpendicularmagnetization film up to 6 nm, and the carbon film up to 10 nm. As tothe Co/Pt multi-layered perpendicular magnetization film, a Co targetand a Pt target were alternately operated to grow a film of 1.5 nm ineach part of one cycle, and thus the total thickness, 6 nm of theperpendicular magnetization film was grown in two cycles. The anisotropyenergy of the Co/Pt multi-layered perpendicular magnetization film was2×10⁷ erg/cc .

Magnetic recording media with no perpendicular magnetization film ofCo/Pt multi-layered film on the medium were also produced as samples forcomparison.

As a result of comparing the measurements under the same read/writeconditions as in Embodiment 3, it was confirmed that the magneticrecording medium according to this embodiment have excellent D₅₀ and S/Nwhich are 40%, 85% higher than the samples for comparison and thus canbe used as high-density magnetic recording medium. In addition, a 2.5-indisk type magnetic recording/reproducing apparatus was produced whichhas a high-sensitive read head (see The Institute of Electronics andCommunication Engineers of Japan, Technical Journal vol. 96, No. 486,pp. 29 to 35) that makes use of magnetic tunnel phenomenon and whichemploys the magnetic recording media produced according to thisembodiment. After the measurement, it was confirmed that under thecondition of area density of 20 Gb/in², the apparatus can attain anerror rate of 1×10⁻⁹ or below and thus can be used as ultra-high densityrecording/reproducing apparatus.

[Embodiment 5]

A Co-35 at % Cr film 20 nm thick was provided on the soft magnetic layerin the magnetic recording medium of embodiment 4. The other portionswere made the same as above. The produced magnetic recording media havethe cross-sectional structure shown in FIG. 5. In other words, on the2.5-in diameter substrate 11, there were formed in turn the softmagnetic layer 42 of Fe—Ni film 30 nm thick, the underlayer 53 of Co—Crfilm 20 nm thick, the first perpendicular magnetization film 13 of Co-19at % Cr-8 at % Pt 30 nm thick, the second perpendicular magnetizationfilm 43 of Co/Pt multi-layered film 6 nm thick, and the protective film15 of carbon film 10 nm thick.

Magnetic recording medium with no perpendicular magnetization film ofCo/Pt multi-layered film under the protective film were also produced assamples for comparison.

As a result of comparing the measurements under the same read/writeconditions as in Embodiment 4, it was confirmed that the magneticrecording medium according to this embodiment have excellent D₅₀ and S/Nwhich are 32%, 60% higher than the samples for comparison.

[Embodiment 6]

A Co/Pt multi-layered perpendicular magnetization film 6 nm thick and aTi film 20 nm thick were provided on and under the soft magnetic layerin the magnetic recording medium of embodiment 4. The other portionswere made the same as above. The produced magnetic recording media havethe cross-sectional structure shown in FIG. 6. In other words, on the2.5-in diameter substrate 11, there were formed in turn the underlayer12 of Ti film 20 nm thick, the soft magnetic layer 42 of Fe—Ni film 30nm thick, the Co—Pt multi-layered perpendicular magnetization film 64 6nm thick, the first perpendicular magnetization film 13 of Co-19 at %Cr-8 at % Pt 30 nm thick, the second perpendicular magnetization film 66of Co/Pt multi-layered film 6 nm thick, and the protective film 15 ofcarbon film 10 nm thick.

Magnetic recording medium with no perpendicular magnetization film ofCo/Pt multi-layered film under the protective film were also produced assamples for comparison. As a result of comparing the measurements underthe same read/write conditions as in Embodiment 4, it was confirmed thatthe magnetic recording medium according to this embodiment haveexcellent D₅₀ and S/N which are 52%, 120% higher than the samples forcomparison.

[Embodiment 7]

The magnetic recording media having the cross-sectional structure shownin FIG. 7 were produced by depositing films on the 2.5-in diameter glasssubstrates according to DC magnetron sputtering method. On the 2.5indiameter substrate 11, there were formed in turn the underlayer 12, theperpendicular magnetization film 71, the soft magnetic layer 72, and theprotective film 15. The underlayer was grown by use of a Ti-10 at % 5 Crtarget, the perpendicular magnetization film by a Co-19 at % Cr-8 at %Pt target, the soft magnetic film by a CoNbZr target, and the protectivefilm by a carbon target. Under the conditions of a sputtering Ar gaspressure of 3 m Torr, sputter power of 10 W/cm², and substratetemperature of 250° C., the CrTi film was deposited up to a thickness of30 nm, the first perpendicular magnetization film up to 30 nm, the softmagnetic film of CoNbZr up to 4 nm, and the carbon film up to 10 nm.

In addition, perpendicular magnetic recording medium with materialsFe—Ni, Fe—Si and Fe—Si—Al used for soft magnetic film 72 were produced.Also, other perpendicular magnetic recording medium were produced whichhave films of Co, Ni—Cr having longitudinal magnetic anisotropydeposited up to a thickness of 4 nm in place of the soft magnetic film72.

Perpendicular magnetic recording medium with the carbon protective film15 directly formed on the perpendicular magnetization film 71 wereproduced as samples for comparison.

The write/read characteristics of these magnetic recording medium weremeasured by the dual head. The gap length of the write head was selectedto be 0.2 mm, the shield gap length of the magnetoresistive (MR) headfor reading to be 0.2 mm, and the spacing for measurement to be 0.06 mm.The half-output recording density (D5o) was measured. The noise in themagnetic recording at 20 kFCI was measured relative to the noise of thesamples for comparison. The measured results are shown in Table 3.

TABLE 3 EXAMPLES FOR COMPARISON EMBODIMENT 1 UNDERLAYER TiCr TiCr TiCrTiCr TiCr TiCr TiCr PERPENDICULAR CoCrPt CoCrPt CoCrPt CoCrPt CoCrPtCoCrPt CoCrPt MAGNETIZATION FILM MAGNETIC FILM No CoNbZr Fe—Ni Fe—SiFe—Si—Al Co Ni—Cr RECORDING DENSITY 155 245 220 210 235 240 225 D₅₀(kFCI) NOISE 1 0.45 0.52 0.38 0.44 0.50 0.37 (RELATIVE VALUE)

From the results, it was found that the magnetic recording mediaaccording to this embodiment have much larger D₅₀ and lower medium noisethan the samples for comparison, and thus can be used as high densitymagnetic recording medium. A 2.5-in disk type magneticrecording/reproducing apparatus was produced by use of the magneticrecording medium produced according to this embodiment and the MR headfor reading. It was confirmed that it assures an error rate of 1×10⁻⁹ ata recording density of 6 Gb/in², and thus can be used as an ultra-highdensity recording/reproducing apparatus.

[Embodiment 8]

The magnetic recording medium having the cross-sectional structure shownin FIG. 8 were produced by depositing films on the 2.5-in diameter glasssubstrates according to DC magnetron sputtering method. On the 2.5indiameter substrate 11, there were formed in turn the first underlayer12, the second underlayer 73, the perpendicular magnetization film 71,the magnetic film 72, and the protective film 15. The first underlayerwas grown by use of a Ti-10 at % Cr target, the second underlayer by aCo-35 at % Cr target, the perpendicular magnetization film by a Co-16 at% Cr-8 at % Pt-3 at % Ta target, the magnetic film by a Fe-80 at % Nitarget, and the protective film by a carbon target. The saturationmagnetization of the Co-35 at % Cr is 20 emu/cc or below, and thus thesecond underlayer is a weak ferro magnetic film. Under the conditions ofa sputtering Ar gas pressure of 3 m Torr, sputter power of 10 W/cm², andsubstrate temperature of 280° C., the CrTi film was deposited up to athickness of 30 nm, the CoCr film up to 15 nm, the perpendicularmagnetization film up to 25 um, the soft magnetic film of FeNi up to 3nm, and the carbon film up to 10 nm. The produced perpendicular magneticrecording media have the cross-sectional structure shown in FIG. 8.

Perpendicular magnetic recording medium with the carbon protective film15 directly formed on the perpendicular magnetization film 71 wereproduced as samples for comparison.

The coercivity (Hc) and write/read characteristics of these magneticrecording media were evaluated by the vibrating sample magnetometer(VSM) and the dual head, respectively. The gap length of the write headwas selected to be 0.2 mm, the shield gap length of the giantmagnetoresistive (GMR) head for reading to be 0.15 mm, and the spacingfor measurement to be 0.04 mm. The half output recording density (D₅₀)was measured. The signal to noise ratio, S/N ratio in the magneticrecording at 20 kFCI was measured relative to the S/N ratio of thesamples for comparison. The measured results are shown in Table 4.

TABLE 4 EXAMPLES FOR EMBODIMENT COMPARISON 2 FIRST UNDERLAYER Ti—CrTi—Cr SECOND UNDERLAYER CoCr CoCr PERPENDICULAR CoCrPtTa CoCrPtTaMAGNETIZATION FILM MAGNETIC FILM No FeNi COERCIVITY He (kOe) 2.5 3.1RECORDING DENSITY D50 185 255 (kFCI) S/N (RELATIVE VALUE) 1 2.3

From the results, it was found that the perpendicular magnetic recordingmedia according to this embodiment have much higher D₅₀ and S/N than thesamples for comparison, and thus can be used as high-density magneticrecording medium. In addition, a 2.5-inch disk type magneticrecording/reproducing apparatus was produced which employs the magneticrecording media made according to this embodiment and the GMR head forreading. It was confirmed that this apparatus can attain an error rateof 1×10⁻⁹ at a longitudinal recording density of 8 Gb/in² and thus canbe used as ultra-high. density recording/reproducing apparatus.

[Embodiment 9]

The magnetic recording media having the cross-sectional structure shownin FIG. 9 were produced by depositing films on the 2.5-in diameter glasssubstrates according to DC magnetron sputtering method. On the 2.5indiameter substrate 11, there were formed in turn the soft magnetic layer74, the multi-layered perpendicular magnetization film 75, the magneticfilm 72 of CoB alloy, and the protective film 15. The soft magneticlayer was grown by use of a Fe-80 at % Ni target, the multi-layeredperpendicular magnetization film by a target of Co and Pt, the magneticfilm of CoB alloy by a Co-6 at % B target, and the protective film by acarbon target. Under the conditions of a sputtering Ar gas pressure of 3m Torr, sputter power of 10 W/cm², and substrate temperature of 250° C.,the FeNi film was deposited up to a thickness of 30 nm, theperpendicular magnetization film of Co/Pt multi-layered film up to 30nm, the CoB magnetic film up to 3 nm, and the carbon film up to 10 nm.Here, as to the Co/Pt multi-layered film as the perpendicularmagnetization film 75, the Co and Pt targets were alternately operatedto grow a film of 1.5-nm thickness in each part of one cycle, and theperpendicular magnetization film having the total thickness of 30 nm wasgrown in 10 cycles.

Perpendicular magnetic recording medium with the carbon protective film15 directly formed on the perpendicular magnetization film 75 wereproduced as samples for comparison.

As a result of comparing the write/read characteristics of thesemagnetic recording medium in the same way as in Embodiment 8, it wasfound that the magnetic recording medium according to this embodimenthave much higher D₅₀ and S/N than the samples for comparison, and thuscan be used as high-density magnetic recording media. In addition, a2.5-in disk type magnetic recording/reproducing apparatus was producedwhich has a high-sensitive read head that makes use of magnetic tunnelphenomenon and which employs the magnetic recording media producedaccording to this embodiment. After the measurement, it was confirmedthat under the condition of area density of 20 Gb/in², the apparatus canattain an error rate of 1×10⁻⁹ and thus can be used as ultra-highdensity recording/reproducing apparatus.

[Embodiment 10]

The Co 35 at % Cr film 73 of 20-nm thickness was provided on the softmagnetic layer 74 in the perpendicular magnetic recording mediumaccording to Embodiment 9. The other portions were the same as above.The produced perpendicular magnetic recording media have thecross-sectional structure shown in FIG. 10. Perpendicular magneticrecording medium with the carbon protective film 15 directly formed onthe perpendicular magnetization film 75 were produced as samples forcomparison. As a result of comparing the characteristics under the samewrite/read conditions as in Embodiment 9, it was confirmed that theperpendicular magnetic recording medium of the invention haverespectively D⁵⁰, S/N 25%, 55% improved higher than the samples forcomparison.

[Embodiment 11]

The present invention will be further described in detail with referenceto FIGS. 11A to 11F.

In FIGS. 11A to 11F, there is shown a. substrate 101 which was an Sidisk with a thermally oxidized Si film formed on the surface. Thesubstrate may be a glass substrate, NiP coated Al substrate, carbonsubstrate or high molecular substrate except the Si substrate. Therinsed substrates 101 were placed in a sputtering apparatus, and theapparatus was evacuated up to 1×10−8 Torr. Then, the substrates 101 wereheated at 230° C. to form an underlayer 102 for controlling the crystalgrain size and magnetic anisotropy of the magnetic films. Any type ofthe underlayer 102 can be selected depending on the kinds of themagnetic film to be formed on this underlayer. The magnetic film can bemade of a material of the hexagonal closed packed structure,body-centered cubic structure, face-centered cubic or rhombic structure.If the magnetic film is made of a material of hcp (hexagonal closedpacked) structure chiefly containing Co, it is possible to mostgenerally select for the underlayer a material chiefly containing anelement of Ti, Ta, Ru, Hf, Co of hcp structure with Cr, V or W added oran amorphous-like material of Si, Ge or others. Also, the underlayer 102may be a single-layered structure of a single material or two ormore-layered structure of different materials. In this embodiment, aTi-10 at % Cr alloy film of hcp structure for the first underlayer wasdeposited on the substrate 101 up to a thickness of 30 nm, and anon-magnetic alloy film of Co-35 at % Cr alloy 20 nm thick was formed onthe first underlayer, thus completing the two-layered underlayer 102.The underlayer 102 has the hcp structure, and its growth orientation<002> was perpendicular to the substrate surface.

Then, the magnetic film for recording and protective film weresuccessively grown on the underlayer in vacuum. For the medium A of thisembodiment according to the invention, as shown in FIG. 11A, a firstmagnetic thin film 103 of a well magnetically isolated material wasdeposited on the underlayer 102, and on this film was formed a secondmagnetic film 105 of which the perpendicular anisotropy constant Ku inthe direction perpendicular to the film surface was larger than thefirst magnetic layer. The magnetic films may be made of a materialcontaining chiefly Co, and additionally at least one of the elements,Cr, Fe, Mo, V, Ta, Pt, Si, B, Lr, W, Hf, Nb, Ru, Ni and rare earthelements. The first magnetic films 103 and 105 may have the same ordifferent crystal structures of thin films. The first magnetic film 103in the medium A may be made of a material additionally containing alarge amount of non-magnetic elements of Cr, Mo, V, Ta, Pt, Si, B, Ir,W, Hf, Nb, Ru, as, for example, Co-17 at % Cr-3 at % Ta alloy or Co-15at % Cr-10 at % Pt-3 at % Ta alloy. The first magnetic film is able toallow the non-magnetic layer or weak ferro magnetic layer locallysegregated within the grain boundaries or grains of the magnetic crystalgrains by the addition of non-magnetic Cr or Ta. By analyzing thecomposition on electron microscope, it was confirmed that the magneticgrains have the effect to improve the magnetic isolation of magneticgrains. In addition, the magnetic anisotropy of the magnetic film can beimproved by adding Pt. The second magnetic film 105 in the medium A maybe, for example, Co-50 at % Pt alloy, Co-20 at % Pt-5 at % Cr alloy, orCo-18 at % Pt-10 at % Cr alloy. The second magnetic film 105 is inferiorto the first magnetic film 103 in the magnetic isolation because it hasless local segregation structure of magnetic layer as compared with thefist magnetic film, but has a larger magnetic anisotropy constant. Themagnetic anisotropy constant Kua of the first magnetic film 103 ofmedium A in the direction perpendicular to the film surface was in therange from 1×10⁶ erg/cc to 4×10⁶ erg/cc, while the magnetic anisotropyconstant Kub of the second magnetic film was in the range from 5×10⁶erg/cc to 1×10⁷ erg/cc. If a material having a larger Ku (more than1×10⁷ erg/cc), for example, Pt/Co multi-layered perpendicular magneticfilm or Pd/Co multi-layered perpendicular magnetic film is used as thesecond magnetic film, the effect of the invention can be furtherimproved. The thickness (t1) of the first magnetic film 103 and that(t2) of the second magnetic film 105 in the medium A according to thisembodiment were t1=30 nm, and t2=20 nm, respectively. If these magneticfilm thicknesses satisfy t1≧t2, another combination of thicknesses maybe used. On the second magnetic film was deposited a carbon (c) film 5nm thick as the protective film 106.

A medium B of another embodiment according to the invention can beconstructed as illustrated in FIG. 11B by depositing on the underlayer102 the first magnetic film 103 of a material of which the magneticisolation is excellent, a non-magnetic intermediate layer 104, thesecond magnetic layer 105 of which the perpendicular magnetic anisotropyconstant Ku in the direction perpendicular to the film surface is large,and then the protective film 106. The materials and thicknesses of thefirst and second magnetic films can be similarly selected as in themedium A. The non-magnetic intermediate layer 104 in the medium B hasthe effect of promoting the epitaxial growth of the second magnetic film105, the effect of suppressing the crystal grains of the second magneticfilm from being enlarged, and the effect of controlling the intensity ofthe magnetic mutual action between the first and second magnetic films.The non-magnetic intermediate layer 104 may be made of the samenon-magnetic material as the underlayer 102, and should be desirablydeposited to have a thickness ranging from one atom layer to 10 nminclusive. It was 5 nm in this embodiment.

Samples of five different media for comparison were produced as shown inFIGS. 11C through 11F. The medium A for comparison, as shown in FIG.11C, was constructed by depositing on the substrate 101 the underlayer102, the magnetic film 103 of a single material 50 nm thick, and theprotective layer 105. Here, the magnetic film was made of the samematerial as the first magnetic film in medium A. The medium B forcomparison, as shown in FIG. 11D, was constructed by depositing on thesubstrate 101 the underlayer 102, the magnetic film 105 of a singlematerial 50 nm thick, and the protective layer 106. Here, the magneticfilm was made of the same high Ku material as the second magnetic filmin medium A. The medium C for comparison, as shown in FIG. 11E, wasconstructed by depositing on the substrate 101 a lower magnetic film107, an upper magnetic layer 108 and then the protective film 106. Here,the lower magnetic film 107 was made of a material having a lowcoercivity (Hc) in the direction perpendicular to the film surface, forexample, 1000 Oe (oersted) or below, or of a material of CoNiReP or NiPin this embodiment. The upper magnetic film 108 was made of a materialhaving a larger coercivity (1000 to 1500 Oe) in the direction

perpendicular to the film surface, for example, CoNiReP, than the lowermagnetic film 107. Here, the coercivity of the thin film was changed bychanging the composition of the material. The medium D for comparison,as shown in FIG. 11F, was constructed by alternately depositingnon-magnetic materials 109 and 110 on the substrate over 50 cycles in astacked manner. The non-magnetic material 109 was Pd and deposited 0.4nm thick as a layer, and the non-magnetic material 110 was Co-15 at %Cr-3 at % Ta alloy and deposited 0.2 nm thick as a layer. The magneticanisotropy constant Ku of this medium in the direction perpendicular tothe film surface was about 8×10⁶ erg/cc. The medium E for comparison, asshown in FIG. 11F same as in the medium D for comparison, wasconstructed by alternately depositing the non-magnetic materials 109,110 on the substrate over 20 cycles in a stacked manner. Thenon-magnetic material 109 was Pt and was deposited 1.2 nm thick as alayer, and the magnetic material 110 was Co and deposited 0.4 nm thickas a layer. The magnetic anisotropy constant Ku of the medium in thedirection perpendicular to the film surface was about 2×10⁷ erg/cc.

Table 5 shows the characteristics of the media of the embodiment of theinvention.

TABLE 5 HALF-OUTPUT Ku RECORDING NOISE N/S₀ COERCIVITY (erg/cc) DENSITYD₅₀ AT 250 kFCI INVENTION MEDIUM SECOND MAGNETIC FILM SECOND MAGNETICFILM 290 kFCI (μVrms/μVpp) A 1800-2100 5 × 10⁶ − 1 × 10⁷ 0.008 FIRSTMAGNETIC FILM FIRST MAGNETIC FILM 1500-2200 1 × 10⁶ − 4 × 10⁶ MEDIUMSECOND MAGNETIC FILM SECOND MAGNETIC FILM 295 kFCI 0.008 B 1800-2100 5 ×10⁶ − 1 × 10⁷ FIRST MAGNETIC FILM FIRST MAGNETIC FILM 1500-2200 1 × 10⁶− 4 × 10⁶ MEDIA A 1500-2200 1 × 10⁶ − 4 × 10⁶ 220 kFCI 0.015 FOR B1800-2100 5 × 10⁶ − 1 × 10⁷ 160 kFCI 0.07 COMPARI- C LOWER MAGNETIC FILM1 × 10⁶ 125 kFCI 0.1 SON <1000 UPPER MAGNETIC FILM 1000-1500 D 2200 8 ×10⁶ 230 kFCI 0.012 E 2000 2 × 10⁷ 175 kFCI 0.05

The values on Table 5 were obtained by using a ring-type inductivemagnetic head (2 μm in track width, 0.2 μm in gap length) for writing,and a magnetoresistive head (MR head) for reading and by setting themagnetic spacing (the distance between the surface of the magnetic filmof the medium and the magnetic pole of the magnetic head) to be 30 nm atthe writing/reading process. I n addition, on Table 5, the half-outputrecording density D₅₀ indicates the linear recording densitycorresponding to half the reproduced signal output at the low linearrecording density (5 kFCI), and its unit was represented by FCI (FluxChange per Inch). Also, the noise N/So is the normalized noise, whichnoise measured at linear recording density 250 kFCI was normalized bythe reproduced signal output at low linear recording density (5 kFCI).From Table 5, it will be seen that the media A and B of the inventionhave an ability of high half output recording density (D₅₀) and lownoise characteristic as compared with the conventional media forcomparison, and thus can be satisfactorily used as media for ultra-highdensity magnetic recording.

The magnetized states of the magnetically recorded samples were observedby a magnetic force microscope (MFM) in order to compare the causes ofthe low noise characteristics of media. FIGS. 12A to 12F show theresults.

FIG. 12A shows one example of the magnetized state of media A, Billustrated in FIGS. 11A and B. The perpendicular magnetic recording wasmade by the ring-type inductive magnetic head after all the mediasurfaces were erased by DC. As illustrated, a recorded magnetic domain132 was recorded on a DC erased region 131. The bright and dark regionsrespectively indicate different average orientations of magnetization.As illustrated, clear recorded magnetic domains 132 were formed in themedia A, B of the invention, and the magnetization transitions 133 hadsmall instability of which the amplitude was as fine as about 30 nm thatis substantially equivalent to the average diameter of the magneticgrains of the media. FIG. 12B shows the magnetized state of medium A forcomparison. In this case, by improving the crystal orientation ofmagnetic thin films, the fine granulation of magnetic material and themagnetic isolation of magnetic grains, it is possible to form clearmagnetic domains with small magnetic transition instability asillustrated in FIG. 12B. However, a large number of magnetizationirregularities 134 having more than twice the magnetic crystal grainsize appear within the Dc erased region 131 and recorded domains 132 asillustrated. The magnetization irregularities 134 are called reversemagnetic domains that are formed in the direction opposite to themagnetizing orientation chiefly by the effect of demagnetizing field.These magnetization irregularities 134 cause media noise at thewriting/reading process, and interfere with high-density recording. FIG.12C shows the magnetized state of the medium B for comparison. In thiscase, the magnetic anisotropy constant of magnetic films was set to belarge, and the mutual action between the magnetic grains is strong.Thus, a very small number of magnetization irregularities occur, but themagnetization transition instability is very great as illustrated. Thismakes the medium noise increase, and causes a barrier against theimprovement in the recording density. FIG. 12D shows the magnetizedstate of medium C for comparison. In this case, both magnetizationtransition instability and large-sized magnetic irregularities occur.FIG. 12E shows the magnetized state of medium E for comparison. In thiscase, the perpendicular magnetic anisotropy constant Ku of the medium isas large as 2×10⁷ erg/cc, and thus clear magnetic domains with nomagnetic irregularity are formed within the DC erased regions 131 andrecorded domains 132. However, the magnetic mutual action betweenmagnetic grains is strong, and thus the magnetization transitions 133have great instability. FIG. 12F shows the magnetized state of medium Dfor comparison. In this case, the magnetization transition instabilityis small, and clear magnetic domains can be formed similar to the mediumof the invention. However, the magnetic irregularities 134 appear withinthe recorded domains 132 and DC erased regions 131.

[Embodiment 12]

One embodiment of magnetic recording apparatus of the invention will bedescribed with reference to FIGS. 13A and 13B.

The perpendicular magnetic recording medium produced by way ofexperiment and the dual head with inductive head for writing and withgiant magnetoresistive (GMR) head for reading were used to produce amagnetic recording/reproducing apparatus shown in FIGS. 13A and 13B.Referring to FIGS. 13A and 13B, there are shown a magnetic recordingmedium 151, a magnetic recording medium drive 152, a magnetic head 153,a magnetic head drive 154, and a signal processor 155.

The magnetic recording medium, or disk 151 was constructed by depositingon a disk-like substrate such as a glass substrate, Si substrate, NiPcoated aluminum substrate or carbon substrate, an underlayer forcontrolling the crystal orientation of a magnetic film, the magneticfilm, and then a protective film. A lubricant film was further coated onthe protective film. The magnetic film contains chiefly Co, andadditionally an element of Cr, Pt, Ti, Ru, Ta, W, Mo, Pd. The magneticeasy axis of the magnetic film was oriented in the directionperpendicular to the substrate surface. In order to obtain theperpendicular recording medium with the magnetic easy axis of themagnetic film oriented in the direction perpendicular to the substratesurface, the underlayer for controlling the structure is made of amaterial of non-magnetic CoCr alloy, Ti, TiCr alloy or of apolycrystalline or noncrystal material with an element of Pt, Ru, Ta,Mo, Pd added to the non-magnetic alloy to produce hcp structure or anamorphous-like material of Si, Ge.

The magnetic head is constructed by a slider, the magnetic poles of amagnetic write head provided on the slider, and a magnetoresistive,giant magnetoresistive, spin valve effect or magnetic tunnel typeelement for reading. In order to reduce the magnetization irregularitiesof the track edges at magnetic writing process, it is desired to alignboth track edges of trailing and leading side magnetic poles of thewrite head. Since the track width of the read head is narrower than thatof the write head pole, the read back noise from both written trackedges can be reduced.

The magnetic head 153 is supported by a suspension 3, and corrected forthe yaw angle caused when the magnetic head is moved from the innerperiphery side of the disk to the outer periphery side.

The track width of the write head, the track width-of the GMR headsensor for reading, and the spacing between the head and the medium wereselected to be 0.4μm, 0.32 μm and 20 nm, respectively. When theapparatus was operated under the conditions of PR 5 system signalprocessing and 36 Gb/in² longitudinal recording density, the error ratewas less than 1×10⁻⁹.

Thus, according to the invention, as described above, since at least twomagnetic films of different perpendicular magnetic anisotropy are formedon the substrate, in which case the perpendicular magnetic anisotropy ofthe second magnetic film of those magnetic films, far from the substratesurface, is selected to be larger than that of the first magnetic filmnear to the substrate surface so as to improve the magnetic isolation ofthe first magnetic film near to the substrate surface, or when adifferent role is assigned to each magnetic film as they say, theproduced magnetic recording media and magnetic recording apparatus canbe improved in such a manner that the magnetization transitioninstability structure and magnetization irregularity structure of therecorded magnetic domains which cause the medium noise can berespectively reduced to be small and completely removed to make the S/Ncharacteristic of the read signal be increased and enough to be suitedfor ultra-high area density magnetic recording. Particularly, it ispossible to make high-density magnetic recording of 5 Gb/in2 or above,and hence to easily produce small-size, large-storage-capacity recordingapparatus.

What is claimed is:
 1. A magnetic recording apparatus comprising: amagnetic head; and a magnetic recording media comprising: a substrate, asoft magnetic film formed on said substrate, a non-magnetic or weakferro-magnetic underlayer of which the saturation magnetization of saidnon-magnetic or weak ferro-magnetic underlayer is less than 100 emu/ccand said underlayer has a hexagonal closed packed structure, a firstperpendicular magnetization film formed on said non-magnetic or weakferro-magnetic underlayer, a second perpendicular magnetization filmformed on said first perpendicular magnetization film, and the thicknessof said second perpendicular magnetization film is less than that ofsaid first perpendicular magnetization film.
 2. A magnetic recordingapparatus according to claim 1, the thickness of said secondperpendicular magnetization film is within a range of 2 to 10 nm.
 3. Amagnetic recording apparatus according to claim 1, wherein said secondperpendicular magnetization film is multi-layered film.
 4. A magneticrecording apparatus according to claim 1, the magnetic anisotropy energyof said second perpendicular magnetization film Kub is grater than orequal to that of said first perpendicular magnetization film Kua.
 5. Amagnetic recording apparatus comprising: a magnetic head; and a magneticrecording media comprising: a non-magnetic substrate, a non-magnetic orweak ferro-magnetic underlayer formed on said non-magnetic substrate,wherein the saturation magnetization of said non-magnetic or weakferro-magnetic underlayer is less than 100 emu/cc and said underlayerhas a hexagonal closed packed structure, a first perpendicularmagnetization film formed on said non-magnetic or weak ferro-magneticunderlayer, a second perpendicular magnetization film formed directionon and in contact with said first perpendicular magnetization film,wherein the magnetic anisotropy energy of said second perpendicularmagnetization film Kub is greater than or equal to that of said firstperpendicular magnetization film Kua, and said second perpendicularmagnetization film is multi-layered film.